1. Field of the Invention
The present invention relates to an optical deflector having a deflection means for deflecting light.
2. Related Background Art
FIG. 1 shows a galvano-mirror which is an example of an optical deflector. This galvano-mirror can be moved by an electromagnetic force. The mirror is located on a movable portion. The movable portion is supported by a main body portion through a torsion bar so as to oscillate about a shaft center. In FIG. 1, reference numeral 50 denotes a silicon substrate, 51 denotes an upper side glass substrate, and 52 denotes a lower side glass substrate. Reference numeral 53 denotes a movable plate, 54 denotes a torsion bar, 55 denotes a flat coil, 56 denotes a total reflection mirror, 57 denotes electrode terminals, and 60 to 63 denote permanent magnets. The optical deflector is an electromagnetic type driven by allowing a drive current to flow into the flat coil 55 to use a Lorentz force produced between the flat coil 55 and the permanent magnets (for example, see Japanese Patent Application Laid-Open No. H07-175005 (pages 3 and 4 and FIG. 1)).
Another example is described in Japanese Patent Application Laid-Open No. 2001-305471 (pages 3 and 4 and FIG. 1). This relates to an electromagnetic actuator. The examples described in Japanese Patent Application Laid-Open No. 2001-305471 and the example described in Japanese Patent Application Laid-Open No. H07-175005 are identical to each other from the viewpoint that the movable portion is moved by an electromagnetic force. The electromagnetic actuator described in Japanese Patent Application Laid-Open No. 2001-305471 also has a total reflection mirror provided in a movable portion.
According to Japanese Patent Application Laid-Open No. 2001-305471, the following problem, objects, and means are described. That is, a resonance period of the electromagnetic actuator is generally drifted with temperature or time. When a current having a preset resonance frequency is continued to supply to the flat coil, a problem in that an oscillating angle is not controlled to be constant with a change in temperature and a lapse of time occurs. While paying attention to this problem, a first object is to provide an electromagnetic actuator which can be moved for reciprocation at a resonance period thereof without a specific drive detection means, a control device for controlling the electromagnetic actuator, and a method thereof. A second object is to provide an electromagnetic actuator whose oscillating angle can be controlled without a specific detection means, a drive control device for controlling the electromagnetic actuator, and a method thereof. A third object is to provide a resonance frequency signal generating device for an electromagnetic actuator which can output a resonance frequency signal corresponding to the resonance period thereof and a resonance frequency signal generating method therefor.
In order to solve the above-mentioned problem, the coil is used for driving the movable portion and also used for detection. An induced electromotive force or an induced current which is produced in the coil is detected.
Japanese Patent Application Laid-Open No. 2001-305471 describes that the resonance period of the electromagnetic actuator is drifted with temperature or time. The coil serving as the detection means is always used for driving. Therefore, a period for applying a drive signal to the electromagnetic actuator is limited.
In Japanese Patent Application Laid-Open No. H07-175005, no attention is given to a problem in that the resonance period is drifted with temperature.